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Feb
19
comment How to get from $a\sqrt{1 + \frac{b^2}{a^2}}$ to $\sqrt{a^2 + b^2}$
Hint: for positive $a$, $a = \sqrt{a^2}$.
Feb
6
comment Time Series and statistics
@Probabilityman Oops, sorry about that.
Feb
6
revised Time Series and statistics
fixed my mistake
Feb
6
suggested approved edit on Time Series and statistics
Feb
6
comment Time Series and statistics
@DilipSarwate Ah sorry, yes I think you're correct. It was previously written as (Xt - j) and I didn't even think about whether it should be X(t)-j or X(t-j). The latter makes much more sense.
Feb
6
revised Time Series and statistics
fixed typos and added latex
Feb
6
suggested approved edit on Time Series and statistics
Jan
18
answered Mathematical toys?
Jan
18
comment Mathematical toys?
Define "serious."
Jan
18
awarded  Fanatic
Jan
16
comment Generalization of variance to random vectors
Note: the covariance matrix contains covariances, not correlations (i.e. the elements are not constrained to $[-1,1]$). Further note: the diagonals of the covariance matrix are variances.
Nov
30
revised finding interval where inequality holds
fixed up the TeX
Nov
30
suggested approved edit on finding interval where inequality holds
Nov
24
answered Puzzle: numerical pattern recognition
Nov
23
answered Ways to teach fractions
Nov
9
awarded  Enthusiast
Nov
4
comment Finding a formula to sum natural numbers up to $n$
I love this trick -- usually blows the mind of at least one student when shown to them. Can you do something similar for the sum of squares, cubes, etc?
Nov
4
comment Working out the variance of the Poisson distribution
Take a look at factorial moments and factorial moment generating functions (That's what he's using).
Nov
2
revised Confused about modular notations
added latex and relevant tags
Nov
2
suggested approved edit on Confused about modular notations